1. Field of the Invention
This invention concerns generally absorptive devices such as disposable diapers and, more particularly, a backing for such devices which retards the passage of liquids while permitting the passage of vapors.
2. Background Art
Absorptive devices such as diapers are well known for their use in absorbing and retaining liquid discharges from the human body. Diapers can be either of the more or less permanent type which are intended to be cleaned and reused a number of times or of the disposable type which are intended to be used only once and then discarded. It is known that the exterior of diapers, particularly of disposable diapers, can be covered with a flexible, impermeable sheet to prevent any absorbed liquid from passing through the diaper and soiling adjacent articles such as clothing, bedding, and the like. These covering sheets are known as backsheets and are generally constructed from a waterproof plastic such as polyethylene. The backsheets do prevent liquid from passing therethrough and do help contain liquid within the diaper. Unfortunately, they also sometimes make the diaper feel hot and uncomfortable to wear because of their total impermeability. In addition, their impermeability precludes self-drying of the diaper which would otherwise occur through evaporation of the liquid contained therein.
Backsheets which are pervious to vapor are known as breathable backsheets and have been described in the art. These breathable backsheets provide a cooler garment and permit some drying of the diaper while it is being worn. In general, these breathable backsheets are intended to allow the passage of vapor through them while retarding the passage of liquid.
For example, U.S. Pat. No. 3,156,242 issued to Crowe, Jr. on Nov. 10, 1964 teaches the use of a microporous film as a breathable backsheet. U.S. Pat. No. 3,881,489, issued to Hartwell on May 6, 1975, teaches a breathable backsheet comprising in combination two layers, the first of which is a low void volume perforated thermoplastic film and the second of which is a porous high void volume hydrophobic tissue. U.S. Pat. No. 3,989,867 issued to Sisson on Nov. 2, 1976 teaches a breathable backsheet provided with tapered hollowed bosses which prevent the passage of liquids while allowing vapors to pass readily therethrough.
While these backsheets do provide some measure of improvement over the more common impermeable backsheets, and while the last two named devices are of particular value, devices providing for the more efficient passage of vapor while still restricting the passage of liquid when subjected to the pressure encountered during normal wearing have still been sought.